1. Technical Field
The present invention relates to a liquid ejecting apparatus. More specifically, the invention relates to a liquid ejecting apparatus that adheres liquid, which is discharged from openings of a nozzle plate mounted on a liquid ejecting head, to a recording object.
2. Related Art
When a liquid ejecting apparatus adheres liquid to a recording object without any remaining margin at the periphery of the recording object, the liquid ejecting apparatus ejects liquid toward an area slightly larger than the size of the recording object in view of an inevitable positional deviation between the recording object and a liquid ejecting head. Thus, liquid is also ejected toward an area where the recording object is not present in proximity to the side peripheries and front and rear peripheries of the recording object. Then, an absorption member is arranged at a position opposed to the liquid ejecting head and located farther from the liquid ejecting head than the recording object, and the absorption member absorbs liquid that has been ejected but not adhered to the recording object. This prevents a stain from adhering to around the recording object due to liquid that has not adhered to the recording object.
In the meantime, when liquid is adhered to a recording object, the recording object may possibly form wrinkles because a portion to which the liquid is adhered may possibly expand. If the wrinkles contact the absorption member, liquid that has been absorbed by the absorption member stains the recording object. Then, in most of the liquid ejecting apparatuses, in view of the heights of wrinkles formed in the recording object, a clearance of about 2 to 4 mm is provided between the recording object and the absorption member. For the same purpose of preventing a stain due to contact, a clearance of about 1 mm is provided between the nozzle plate and the recording object. Thus, about 3 to 5 mm clearance is provided between the nozzle plate and the absorption member.
On the other hand, for the purpose of improving resolution of an image that is formed on the recording object by liquid, liquid droplets discharged from the openings of the nozzle plate tend to become finer and finer. When focusing on a single liquid droplet, the amount of the liquid droplet is only about a few picoliter. These fine liquid droplets each have an extremely small weight, so that, when the liquid droplets are once discharged from the nozzle plate, they rapidly lose their kinetic energy due to the viscous drag of the atmosphere, or the like. For example, it has been proved that liquid droplets having an amount of less than 8 picoliter lose their velocity to substantially zero when they fly a distance of about 3 mm in the atmosphere. The fine liquid droplets that have thus lost kinetic energy need a relatively long time until they complete falling because falling motion due to gravitational acceleration becomes substantially equal to a viscous drag force of the atmosphere. Liquid droplets float in the air until they complete falling. These liquid droplets are termed as aerosols.
Some of the thus produced aerosols float to the outside of the liquid ejecting apparatus and adhere to a peripheral area. In addition, most of the aerosols adhere to portions within the liquid ejecting apparatus. When the aerosol adhere to a path, such as a platen, along which a recording object is transported, a recording object that will be transported for the next time is stained because the aerosols adhere again to the next recording object. Further, when the aerosols are adhered to an electrical circuit, a linear scale, a rotary encoder, an optical sensor, or the like, which are mounted in the liquid ejecting apparatus, it may cause malfunction of the liquid ejecting apparatus itself. Furthermore, when a user touches the portions to which the aerosols are adhered, user's hand will be smeared with the aerosols.
Japanese Unexamined Patent Application Publication No. 2004-202867 describes a liquid ejecting apparatus that has the function of actively collecting aerosols using an electric field. In the liquid ejecting apparatus described therein, for the purpose of adhering and absorbing liquid droplets that have not adhered to a recording object, an absorption member is arranged at a position opposed to a nozzle plate. In addition, a metal component, which serves as a first electrode, is arranged on the surface of the absorption member, and a metal nozzle plate having openings for ejecting liquid is used as a second electrode.
When these electrode and nozzle plate are applied with different voltages, an electric field is generated therebetween. On the other hand, liquid droplets discharged from the nozzle plate, at the moment when the liquid droplets are discharged from the nozzle plate, will be charged with the same pole as that of the nozzle plate owing to a so-called lightning rod effect. Thus, fine liquid droplets, which may become aerosols, also continue flying toward the electrode without any deceleration owing to Coulomb attraction from the electric field and are then adsorbed by the electrode having an electric potential that is opposite in pole to those of their own electric charge. Furthermore, liquid droplets that are adsorbed by the electrode are absorbed by the absorption member, which is arranged in proximity to the electrode, by the action of capillarity.
As described above, it has been proved that it is possible to suppress production of aerosols by means of an electric field utilizing the aerosols being electrically charged. However, in the liquid ejecting apparatus having the above described function, there is another technical problem to be solved because of the structure that the electrodes are arranged in a space between the nozzle plate and the platen, in which the space is physically restricted in layout.
That is, the clearance between the nozzle plate, which ejects liquid, and the recording object is preferably smaller within a range in which the nozzle plate and the recording object do not contact each other. Thus, a platen that supports the recording object to that position is also arranged in proximity to the nozzle plate. In addition, the absorption member accommodated in the platen is also preferably arranged in proximity to the nozzle plate within a range in which the absorption member does not contact the recording object. For this reason, a space that is left just below the nozzle plate is extremely small.
On the other hand, when the electrode, which is arranged in proximity to the absorption member, is directly opposed to the nozzle plate, liquid may adhere to the electrode, and an electric field formed between the nozzle plate and the electrode thereby may possibly vary. Then, the electrode is arranged behind the absorption member relative to the nozzle plate and, as a result, the electrode may be extended outside from the accommodation portion of the platen. However, as described above, because the clearance between the nozzle plate and the platen is small, a component, when passed over the side wall of the accommodation portion of a platen body, interferes with the nozzle plate. For this reason, a structure is employed in which the side wall of the accommodation portion has a cutout portion formed therein and a component that connects the electrode to an external is passed through the cutout portion.
However, since the side wall has a low height at a portion where the cutout portion is formed, when liquid absorbed by the absorption member increases, ink may overflow outside through the cutout portion. Because liquid contains electrolyte and thus has conductivity, a short circuit may occur when liquid that has overflown to the outside of the platen adheres to a component having an electrical function, such as the electrode. Moreover, because most types of liquid promote corrosion of a metal component, it is undesirable that liquid adheres to the metal component.